Polymers of vinylidene monomers, destaticized with dihydroxyethyl ethylene diamine



2,891,031 Patented June 16, 1959 POLYMERS F VINYLIDENE MONOMERS, DE-STATICIZED WITH DIHYDROXYETHYL ETHYL- ENE nmMiNE 5 Myron A. Coler,Scarsdale, 'and Arnold S. Louis, Riverdale, N .Y. N0 Drawing.Application March 30, 1956 Serial No. 574,953

13 Claims. (Cl. 260-32.6)

This invention relates to improved synthetic resin molding compositionsand, in particular, to such molding materials which avoid the highlyundesirable effects of electrostatic charge build-up during the moldingoperation, and method of making same.

it has been found that the process of molding certain synthetic resinscauses the generation of high electrostatic charges. This evidencesitself frequently by the formation of crows feet, fern-like and zig-zagpatterns through the attraction of fine dust particles from theatmosphere. Such patterns are sometimes erroneously interpreted as beingmolding flaws.

The literature discloses many additives for rendering synthetic resinsdestaticized. Many of such additives depend on the property ofdeliquescence to cause the article to be wetted by moisture from theair. The moisture renders the surface of the article sufliciently conductive to prevent the further accumulation of electrostatic charges.Molding operations are normally carried out at temperaturessubstantially in excess of the boiling point of water and, therefore, asmolded, the molded article is moisture free and thus subject to theaccumulation of electrostatic charges at the time of molding.

Still other additives which are inherently destaticizing agents tend toundesirably aifect the physical properties of the plastic. For example,a lowering of the heat distortion point may occur, there may also be achange in color, gloss, hardness, or water absorption, or blemishes mayresult from decomposition of additives or evaporation of low boilingfractions. The resulting product may also become toxic if the additiveis in itself toxic. Color is an important factor because a sizeablevolume of the synthetic resins produced reaches the consumer in a clearor tinted translucent form. It may be appreciated that but few materialsare so compatible with clear plastics such as polystyrene that they maybe incorporated without affecting the clarity or color of the moldedplastic.

Our invention, disclosed hereinafter, provides a plastic compositionwhich avoids the disadvantages of acquiring electrostatic charges and,in particular, which is not susceptible to electrostatic charging duringthe molding operation. This invention does not depend on deliquescentaction and, therefore, produces results substantially independent ofhumidity. This advantage of this invention is important in theelimination of dust patterns from freshly molded plastic articles.

We have found that a particular additive, N,N,di(2- hydroxyethyl)ethylene diamine (referred to hereinafter as the additive), which is ahighly polar compound, is compatible with polystyrene which is butslightly polarized. That the materials are so compatible as not todestroy the clarity and translucency of the plastic is an interestingresult in view of the difference in polarization. By incorporating theabove mentioned additive in polystyrene, the desired destaticizingproperties are attained without incurring any of the undesirablefeatures enumerated above. The quantity of additive employed is between1 and 5 percent by weight of the total and preferably between 2 and 4percent. The upper limit is a matter of choice dictated byconsiderations of economy and is not critical. For example, 10 percentor more may be used and the desired destaticizing results obtained.Although at higher concentrations there is danger of aflecting physicalproperties adversely.

A totally unexpected advantage of the above named additive wasdiscovered during molding tests: of material prepared in accordance withthis invention. It was found that the additive improved flow propertiesof the base plastic so as to permit shorter molding cycles as well asimproved filling of thin mold sections, reduced breakage of thin-walledmoldings and easier mold release.

An object of this invention is, therefore, to provide a method foreliminating the formation of electrostatic charges on molded plasticarticles.

Another object is to provide a plastic molding composition havingimproved molding properties and a method of making same.

Still another object is to provide a plastic molding composition havingpreferred flo w properties when injection molded.

A particular object is to provide a translucent plastic material whichis substantially non-susceptible to acquiring electrostatic charges.

A particular object of this invention is to provide a method foreliminating the formation of electrostatic charges on molded plasticarticles during the molding operation.

Another object is to provide articles comprising polystyrenecompositionswhich are free ofthe effects of electrostatic charges.

Another object is to provide a plystyrene molding composition suitablefor molding translucent articles free from the effects of electrostaticcharges.

Still another object of this invention is to provide an improved plasticcomposition.

A still different object is to reduce the electrostatic charge onpolystyrene objects made by injection molding.

A further object of this invention is to provide a polystyrenecomposition of superior molding properties.

Further objects and advantages will become apparent and still otherswill be pointed out with particularity as the following detaileddescription proceeds.

In order to illustrate the invention, specific examples are providedhereinafter. It is to be understood that they are not to be regarded aslimiting in any way but merely illustrative.

Example 1 0.2 pound of the additive, as supplied by Visco ProductsCompany was dissolved in one pound of isopropyl al cohol. 9.8 pounds ofMonsanto Chemical Corporation L2020 PIX-6 polystyrene granules, having aparticle size ranging from about 60 to 10 mesh, were then thoroughlymixed with the solution. The alcohol was then evaporated in an exhaustoven at 65 C. for 36 hours with occasional agitation so as to leave thepolystyrene granules uniformly coated with said additive.

The coated material was then fed through a Windsor type RC-65 twinscrewextruder equipped with a series of A." square orifices. The die wasmaintained at 400 F. The extruded material was chopped up into moldinggranules.

Whereas the coated granules were sticky to the touch, the choppedgranules were dry and free flowing and indistinguishable from untreatedpolystyrene molding chips.

The molding granules were injection molded on a Reed- Prentice 8 ounceinjection molding press with a heater temperature of 600 F. Theresulting articles were promptly sprayed with line bentonite dust bymeans of a The dust did not collect in patterns or charged areas;Additional moldings were set aside and observed periodically for severalweeks. The absence of dust patterns was. noted. Using a Keithleyelectrostatic voltmeter, a' potential of less than one volt was measuredbetween a molding and ground immediately after withdrawal from the mold.

As a control means, identical articles were molded from the samepolystyrene not using the additive. One control article was sprayed withthe bentonite dust immediately after molding and a well definedfern-like pattern was immediately apparent. The same control articleyielded a 20'volt reading on the electrostatic voltmeter upon removalfrom the mold. After long term storage another unmodified polystyrenemolding showed definite dust patterns whereas the modified polystyrenearticle showed but few'isolated' gravity deposited grains.

The molding characteristicsof the modified polystyrene was judged to besuperior to that of the control or unmodified polystyrene by the moldingmachine operator on the basis of obviously improved ease of mold releaseand lower breakage of thin-walled moldings.

hand sprayer.

Example 2 The procedure of Example 1 was repeated with the exceptionthat 0.01 gram/pound of phthalocyanine blue was suspended in the alcoholand put through a colloid mill together with the additive prior toincorporation into the polystyrene. The resulting molded product was anattractive clear translucent blue color.

Example 3 1 pound of isopropyl alcohol and 0.3 pound of the additivewere mixed together to form a solution of watery consistency. Theforegoing mixture was worked in a sigma blade mixer with 9.7 pounds ofthe same polystyrene as employed in Example 1. After 10 minutes theparticles were found to be coated with the additive. The coatedparticles were then dried at 65 C. for 24 hours to remove the alcohol.The coated particles were then put through the extruder, chopped andmolded as in Example 1. The resulting products showed the sameproperties as the modified compositions of Example 1.

Example 4 0.3 pound of the additive and 9.7 pounds of the polystyrenewere thoroughly mixed in a sigma blade mixer. The mixture was thenextruded, chopped and molded as in Example 1. The molded articles showedno discernable electrostatic charge as measured on the Keithley meter.The molded articles showed no tendency to collect dust in patternsduring the storage test.

Example 5 Example 4 was repeated with an additive concentration of 1% byweight of the total. The resulting molding exhibited poornon-electrostatic properties, as measured by the Keithley voltmeter. Asmall amount of dust was collected in patterns after storage for twoweeks.

Example 6 The procedure of Example 4 was repeated with an extruder dietemperature of 375 F. utilizing polymethylmethacrylate as supplied by E.I. DuPont de Nemours & Company, Incorporated as the resinous polymer.The resultant molding was cloudy and exhibited excellent anti-staticproperties. The voltmeter reading of a freshly molded article was only2.5 volts.

Example 7 The procedure of Example 4 was repeated with an e'xtruder dietemperature of 350 F. utilizing A3" polyethylene pellets as supplied byE. I. DuPont de Nemours & Company, Incorporated as the resinous polymer.The resultant molding had substantially the same appearance as anunmodified control molding and exhibited excellent non-static andmolding properties. The Keithley voltmeter reading was 0.5 volt directlyafter molding operation.

Example 8 The procedure of Example 4 was repeated using 0.4 pound ofadditive, 9.6 pounds of'polyvinylchloride and a die temperature of 390F. The resulting molded articles were similar in appearance tounmodified polyvinylchloride and exhibited excellent molding andanti-static properties. The electrostatic voltmeter test yielded areading of about 2 volts upon molding.

Example 9 Example 10 The procedure of Example 4 was repeated using 5% ofadditive. The anti-static properties of the resulting molding weresubstantially as in Example 4 but a faint haze appeared in theunpigmented plastic.

Thus far a number of examples have been given which illustrateprocedures which are particularly advantageous where chipped or extrudedplastic is to be mixed with the additive or where the method ofpolymerization in use does not suit the methods of incorporation to bedescribed hereinafter. For most purposes, the procedure of Example 4 isprefered for its simplicity and lack of a separate drying operation.Where a pigment is to be added, the method of Example 2 is preferred.This method is claimed in our copending application entitled Process ForMaking Plastic Compositions, Serial Number 532,132, filed September 21955.

Among the foregoing and following examples several suitable methods ofincorporation are described. The sole critical feature appears to be therequirement that the additive be uniformly dispersed.

In plants where bulk polymerization is practiced, the procedure ofExamples 13 and 14 will be preferred as eliminating several later steps.

Be it observed that it will often be advantageous to prepare a masterbatch of resin with incorporated additive, said master batch containingfar more additive than is recommended for use in molding operations, andbeing later cut back by extrusion or by being otherwise blended withuntreated resin. Such a concentrate may well be sold, particularly inthe clear or natura color for blending with untreated resin of variouscolors or of its own color. For preparing such master batches, themethods of Examples 12 and 14 are preferred. The" master batch maycontain up to 50% additive.

Example 11 30 grams of the additive dissolved in 75 grams of water wereincorporated with 666 grams of polystyrene emulsion containing 30%polystyrene solids.

770 grams of granulated polystyrene were placed in a Baker-Perkinsmixer. With the mixer in operation, the polystyrene emulsion additivemixture was slowly added. The resultant slurry was then dried at 65 C.for 48 hours at which time it was found to be water-free. The resultantmixture which contained 5% of the additive when molded as in Example 1,yielded moldings which when tested as in Example 1, exhibiteddestaticized characteristics similar to the modified product of Example1.

Example 12 styrene emulsion. This mixture was spray-dried to give a freeflowing polystyrene powder containing one part of the additive to threeparts of polystyrene. The resultant concentrate was later tumbled with850 grams of a granulated polystyrene. The resultant blend was injectionmolded under conventional polystyrene molding conditions and yieldeddestaticized moldings have properties comparable to those produced bythe procedures of Example 1.

Example 13 2.4 grams of o e'-azodiisobutyronitrile was dissolved in 970grams of monomeric styrene, 30 grams of the additive were dissolved inthe styrene and the solution was placed in a heated reaction kettle intowhich nitrogen was bubbled. The solution was heated at 70 C. for 1 /2hours until an exothermic reaction took place. The reaction wascontinued for an additional 30 minutes during which the temperature wasgradually increased to 90 C.

Considerable polymerization took place as evidenced by an increase inviscosity. The mixture was transferred to air-free containers which werethen sealed. The containers were maintained at a temperature of 90 C.for 48 hours. The resulting polymer was extruded, chopped and injectionmolded under normal polystyrene molding conditions. Moldings were clearand in all respects comparable to those of Example 4.

Example 14 2.0 grams of 11,11 azodiisobutyronitrile was dissolved in 800grams of monomeric styrene, 200 grams of the additive were dissolved inthe styrene and the solution was placed in a heated reaction kettle intowhich nitrogen was bubbled. The solution was heated at 70 C. for 1 /2hours until an exothermic reaction took place. The reaction wascontinued for an additional 30 minutes during which the temperature wasgradually increased to 90 C. Considerable polymerization took place asevidenced by an increase in viscosity. The mixture was transferred toair-free containers which were then sealed. The containersweremaintained at a temperature of 90 C. for 48 hours. The resultant polymerwas extruded and chopped into granules. Later, 150 grams of the granuleswere mixed with 850 grams of untreated polystyrene molding compounds andextruded, chopped and injection molded under normal conditions forpolystyrene. The quality of the resulting moldings was in all respectsequal to that of the moldings of Example 1.

Thus we have disclosed that by incorporating a minor proportion of N,N'di (2-hydroxyethyl) ethylene diamine in thermoplastic synthetic resinsmany advantages are obtained such as improved molding properties andfreedom from the formation of electrostatic charges. In combination withpolystyrene, clean translucent products are obtained.

For the purpose of illustrating the invention, examples have been shownof the application of our invention to plastic alloys of polystyrene,polyethylene, polyvinylchloride and polymethylmethacrylate and theircopolymers. We wish it to be understood that the invention likewise maybe utilized in treating others such as polyacrylonitrile,polyfluoroethylene, polytrifiuoromonochloroethylene, polybutadiene,halogenated polystyrenes, and mixtures and copolymers of thesematerials.

The term vinylidene as used herein is intended to define monomerscontaining a polymerizable unsaturated ethylenic structure and isgeneric to vinyl and vinylidene monomers. Each of the polymersspecifically exemplified in the preceding examples, namely: polystyrene,polymethylmethacrylate, polyvinyl chloride and polyethylene is a polymerof a vinylidene monomer, so defined.

By plastic alloy as used herein we intend to encompass compositionscomprising two or more types of polymeric molecules whether prepared bycompolymerization or simple mixture.

Several examples have been given herein of suitable methods ofincorporating the additive. The sole critical feature appears to be therequirement that the additive be uniformly dispersed.

While we have disclosed what is at present considered the best mode forcarrying out our invention we appreciate that it will be obvious tothose skilled in the art that various changes and modifications may bemade therein without departing from the invention and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A composition of matters consisting of a thermoplastic polymer of avinylidene monomer and between 1% and 5% by weight of N,N, di(Z-hydroxyethyl) ethylene diamine.

2. The composition of claim 1 wherein is polymethylmethacrylate.

3. The composition of claim 1 wherein said polymer is polyethylene.

4. The composition of claim 1 is polyvinylchloride.

5. The composition of claim 1 wherein said polymer consists of a mixtureof butadiene polymer and polystyrene.

6. A composition of matter consisting of a thermoplastic polymer of avinylidene monomer and from 2 to 4% by weight of N,N di (Z-hydroxyethyl)ethylene diamine.

7. The composition of claim 6 wherein said polymer is polyvinylchloride.

8. The composition of claim 6 wherein said polymer ispolymethylmethacrylate.

9. The composition of claim 6 wherein said polymer is polyethylene.

10. The composition of claim 6 wherein said polymer consists of amixture of butadiene polymer and polystyrene.

11. A composition for molding transparent plastic articles consisting ofpolystyrene and from 1 to 5% by weight of N,N' di (2- hydroxyethyl)ethylene diamine.

12. A composition for molding transparent plastic articles consisting ofpolystyrene and from 2 to 4% by weight of N,N di (Z-hydroxyethyl)ethylene diamine.

13. A transparent molded article consisting of poly styrene and between1% and 5% by weight of N,N' di (2-hydroxyethyl) ethylene diamin saidpolymer wherein said polymer References Cited in the file of this patentUNITED STATES PATENTS 2,403,960 Stoops et a1. July 16, 1946. 2,450,552Hurdis Oct. 5, 1948

1. A COMPOSITION OF MATTERS CONSISTING OF A THEMOPLASTIC POLYMER OF AVINYLIDENE MONOMER AND BETWEEN 1% AND 5% BY WEIGHT OF N,N'', DI(2-HYDROXYETHYL) ETHYLENE DIAMINE.